The natural immune system has evolved to make antibodies for efficient neutralization of pathogens. Natural antibody preparations isolated from immunized animals are polyclonal in origin, and exhibit immunodominance as compared to individual antibodies, which are restricted to one or a few epitopes of a particular antigen. Anti-tumor antibodies are able to block growth or kill tumor cells to which they bind have been developed as highly effective cancer therapeutic agents. Mixtures of anti-tumor antibodies may achieve tumor suppressive effects that are greater than achieved by any individual antibody in the mixture
Such results have been achieved by combining two or more neutralizing antibodies against the epidermal growth factor receptor, EGFR (ErbB1). Antibodies that bind to and inhibit EGFR have proven to provide useful anti-cancer benefits and are of great medical and commercial value. Particular combinations of pairs of antagonistic, yet non-competitive, anti-EGFR antibodies resulted in downregulation of EGFR which was faster and more effective than application of either antibody alone (Friedman et al. (2005) PNAS 102:1915-1920). The combination of two cross-competitive (i.e., competitive with each other for binding to antigen) anti-EGFR antibodies has shown to be non-synergistic. It is possible that binding of a plurality of antibodies to distinct epitopes of EGFR forms lattices of complexed receptors on cell surfaces, leading to more efficient internalization and degradation than obtained with antibodies targeting a single epitope. The combination of a particular pair of anti-EGFR receptor antibodies have also been reported to result in additive and in some cases synergistic, antitumor activity in vivo (Perera et al. (2005) Clin Cancer Res 11:6390-6399). Monoclonal antibody 806, raised against the mutant de2-7 EGFR, combined with antagonistic antibody 528 displayed significantly higher anti-tumor activity in a glioma xenograft model than treatment with either antibody alone. The mechanism of the synergistic anti-tumor activity was shown to be associated with rapid downregulation of EGFR, which was not induced by treatment with the individual antibodies. Similarly EGFR phosphorylation was greatly reduced in the presence of another pair of anti-EGFR antibodies, cetuximab and EMD55900 (Kamat et al. (2008) Cancer Biol Ther 7:726-33).
Certain combinations of antibodies targeting the related receptor, ErbB2, have also been shown to function in synergy (Friedman et al. (2005). Trastuzumab combined with pertuzumab inhibited the survival of BT474 breast cancer cells at doses in which individual antibodies are ineffective (Nahta et al. (2004) Cancer Res 64:2343-2346). In another study three non-competitive anti-ErbB2 antibodies demonstrated far more effective in vitro killing of BT474 cells in combination than individually and similar results were obtained in a BT474 in vivo xenograft model (Spiridon et al. (2002) Clin Cancer Res 8:1699-701).
Other evidence that combining more than one antibody may enhance the growth suppressive (e.g., cytotoxic) effect of antibodies on tumor cells has been reported. For example, monoclonal antibodies to the tumor antigen 17-1A were combined, tumor cell lysis was studied, and it was found that monoclonal antibodies, as well as combinations of competing antibodies, were ineffective, whereas combinations of two or more non-competing antibodies resulted in complete tumor cell lysis.
In addition to combining antibodies, higher antibody potency has also been achieved by increasing the antigen affinity of recombinantly expressed anti-tumor antibodies through recombinant DNA techniques known as affinity maturation.
Accordingly, additional approaches and methods for producing anti-tumor antibody action so as to enhance the responsiveness of tumors to anti-EGFR antibodies and antibody combinations are still needed, including anti-EGFR antibodies with higher tumor affinity and combinations of such high-affinity anti-EGFR antibodies that enhance signaling inhibition and provide more effective cytostatic or cytotoxic anti-tumor outcomes.